Hydration Structure of Na plus and K plus Ions in Solution Predicted by Data-Driven Many-Body Potentials

The hydration structure of Na+ and K+ ions in solution is systematically investigated using a hierarchy of molecular models that progressively include more accurate representations of many-body interactions. We found that a conventional empirical pairwise additive force field that is commonly used in biomolecular simulations is unable to reproduce the extended X-ray absorption fine structure (EXAFS) spectra for both ions. In contrast, progressive inclusion of many-body effects rigorously derived from the many-body expansion of the energy allows the MB-nrg potential energy functions (PEFs) to achieve nearly quantitative agreement with the experimental EXAFS spectra, thus enabling the development of a molecular-level picture of the hydration structure of both Na+ and K+ in solution. Since the MB-nrg PEFs have already been shown to accurately describe isomeric equilibria and vibrational spectra of small ion-water clusters in the gas phase, the present study demonstrates that the MB-nrg PEFs effectively represent the long-sought-after models able to correctly predict the properties of ionic aqueous systems from the gas to the liquid phase, which has so far remained elusive.

Automated summary

The study systematically investigated the hydration structure of Na+ and K+ ions in solution by progressively including many-body effects derived from the many-body expansion of the energy. It found that MB-nrg potential energy functions achieved nearly quantitative agreement with the experimental EXAFS spectra, providing accurate models for predicting properties of ionic aqueous systems from gas to liquid phase.